Grinding wheel dressing apparatus



Dec. 26, 1950 J. C. WILSON GRINDING WHEEL DRESSING APPARATUS Filed Sept. 7, 1946 2 Sheets-Sheet 1 INVENTOR JOHN C.WILSON BY um/UM ATTORNEYS Dec. 26, 1950 Filed Sept. 7, 1946 J. c. WILSON 2,535,183

GRINDING WHEEL DRESSING APPARATUS 2 Sheets-Sheet 2 30 64 6mm mm 62 x 6 My; mm: 68 66 4 mvzm'on JOHN C. WILSON arronusva Patented Dec. 1880 2,535,183 camnmc WHEEL rmassmc APPARATUS John C. Wilson, Springfield, hio, assignor to The Thompson Grinder Company, Springfield, Ohio, a corporation of Ohio Application September I, 1946, Serial No. 695,382

1 7 Claims.

This invention relates to methods and ap paratus in connection with grinding machines, and more particularly in connection with the dressing cycle for forming a grinding wheel in a grinding machine.

One of the preferred methods of forming a grinding wheel is by a crushing roller, a process wherein 'a relatively hard metallic roller is formed to have a cross-sectional contour the same as that it is desired to grind on the WOIk-r piece. With the roller so formed, it is brought into pressure engagement with the grinding wheel and the two are then run together with no slipping therebetween so that the grinding wheel is shaped by being crushed by the roll. The crushing occurs in the bonding of the wheel due to the pressure of the roll bearing thereagainst. Wheels crushed according to this method grind workpieces with a high degree of accurac and with a very smooth surface finish, and the wheel can be maintained accurately dressed for long periods of time by a single roll.

One of the difliculties heretofore encountered in a dressing operation of this type was that of running the wheel and roll together at the proper speed and without any slipping so that the roll was not ground away by the wheel during dressing. In the case of small and light wheels, it is possible satisfactorily to perform a dressing cycle by driving the roll while the wheel driving motor is de-energized. With heavy grinding wheels, having large drive motors connected therewith, there is sufficient inertia in the wheel and motor, together with the friction in the bearings in which the drive shaft rotates, for there to be slipping between the wheel and the roll when the latter is driven.

One way of overcoming this difficulty in order to prevent slipping between the wheel and roll is to mount the roll on anti-friction bearings and to drive the wheel at the necessary reduced speed.

In carrying out a crush dressing cycle by driving the wheel at reduced speed, it is necessary to provide an auxiliary motor, or to provide means for driving the wheel motor itself at reduced speed. It is with the last mentioned means that the present invention is concerned.

In particular, this invention is concerned with means for driving a large and high speed direct current motor at low speeds and for supplying an adequate amount of power thereto during the low speed driving thereof. The preferred way of doing this is by supplying a. low voltage to the motor armature. This supply, however, must be of large capacity and of a substantially constant voltage.

It is an object of this invention to provide an electric circuit operable to supply direct current power to a high speed direct current motor so that the said motor operates at a predetermined lower speed, the power supply during that time originating from an alternating current source.

A still further object of this invention is to provide a control circuit for use in connection with a grinding machine having a crush dressing roll which is operable automatically to drive the grinding wheel at low speed, while automatically advancing the wheel and roll together for a dressing cycle.

These and other objects and advantages will become more apparent upon reference to the following description taken in connection with the accompanying drawings in which:

Figure 1 is a diagrammatic view showing a typical grinding machine having a circuit according to this invention and being adapted for carrying outthe methods thereof; and

Figure 2 is a diagram of the electrical circuit of this invention.

General arrangement In general, this invention concerns a means for supplying direct current power at reduced voltage to the armature of a direct current motor while maintaining substantially the same energization of the field thereof so that the motor will operate at reduced speed. The supply of low voltage direct current originates from a rectifier which is supplied from the secondary of a step-down transformer, the primary of which is connected to alternating current power lines of commercial voltage.

A control circuit is provided which interrupts the supply of direct current at high voltage to the armature of the wheel motor, thereafter dynamically brakes the said armature to a reduced speed, and finally int rrupts the braking circuit while connecting the said armature with the output terminals of the aforementioned rectifler.

When the control circuit is actuated to accomplish th connecting of the wheel motor armature with the rectifier output terminals, there is also automatically energized mechanism for feeding the grinding wheel and roll together to perform a dressing cycle. After a predetermined feeding together of the roll and wheel, a suitable means is actuated which halts the grinding cycle and disconnects the motor armature from the rectifier.

Structural arrangement Referring to Figure 1, there is shown a grinder having a bed It) upon which is reciprocable a table l2 as by the double acting fluid motor [4 carried in the said bed.

Fixed relative to the bed is a column I6 on which is vertically reciprocable a saddle l8 which supports a wheel head structure 28 for transverse movement relative to the aforementioned bed and table. The saddle I8 is adjustable vertically by means of a nut and screw mechanism 22 which is actuated by a shaft 24 carrying a hand wheel 26 and a ratchet 28. The wheel head mechanism 28 includes a. direct current drive motor 38, shown in Figure 2, which is directly connected with the grinding wheel 32. The grinding wheel 32 is adapted for grinding a workpiece 34 carried on the table l2, and for being dressed by the roll 36 when brought together therewith under pressure.

The reciprocation oi the table 42 in order to pass the workpiece 34 beneath the wheel 32 may be controlled by suitable conventional valve mechanisms connected with the lever 38 which is adapted for being shifted by the dogs 4|] carried on the underside of the table I2.

The saddle l8 may be automatically lowered to advance the grinding wheel into the work a predetermined amount on each reciprocation of the table l2 by the pawl mechanism indicated at 48' which, when moved rightwardly by the energization of the solenoid 42 engages one of the teeth 44 on the ratchet wheel 28 and indexes the said wheel a predetermined amount. De-energlzation of the solenoid 42 permits the spring 46 to return the pawl mechanism to the position shown in the drawings.

The solenoid 42 is connected between the power lines L3 and L4 through the blades Cl which are normally held closed by a spring 48 and which are adapted for being opened by the energlzation of the solenoid 0. Also in series with the solenoid 42 is a limit switch LS3 which is adapted for being closed by the cam 50 as the table approaches one limit of its travel during the grinding of a workpiece.

The total down-feed of the saddle I8 is controlled by one or the other of the parallelly connected limit switches LSI and LS2, which are connected in series with the solenoid C in order to energize the latter when either of the said switches are closed. The switch LSI is adapted for being closed by the cam 52 carried on the saddle l8 when the wheel head has advanced a predetermined amount, while the limit switch LS2 is adapted for being closed by the cam 54 which is adjustably carried on the ratchet wheel 28.

The solenoid 42, for effecting the downfeed of the grinding wheel, is also adapted for being energized by the closing of a switch SI which is arranged to be alternately closed and opened by a cam 56 carried on the shaft of a motor 58. The motor 58 is an adjustable speed motor, having the speed adjusting rheostat 60 in association therewith.

Referring to Figure 2, it will be seen that the wheel head motor, which is generally indicated at 38, is adapted for being supplied with power from direct current supply lines L3 and L4. Connected between these lines is the shunt field coil 62, in series with which there may be an adjustable rheostat 64 for adjusting the field lilr strength of the motor. Also connected between the lines L3 and L4 is the motor armature 66 in series with which is the series field winding 68, and the normally closed contactor blades A2.

shunted across the motor armature is a dynamic braking resistor 10 in series with which are the normally open contactor blades A3 and the normally closed contactor blades B3.

In Figure 2 there is also shown a step-down transformer I2 having a primary 14 connected with the alternating current power lines L5 and L6, and also having a secondary winding 16 connected with the opposite terminals of a full wave rectifier bridge generally indicated at 18. The other corners of the bridge 18 are connected one with the line L4 by a wire 88, and the other through the normally open contactor blades B2 with the junction point of the blades A2 and the series field coil 68.

The circuit shown for the purpose of controlling the energization of the contactors A and B, will be seen to comprise a pair of power lines L3 and L4 between which are connected the contactor A in series with the normally closed switch 82 and the normally open switch 84. The switch 84 is bypassed by the normally open blades Al. The switches 82 and 84 together are bypassed by a normally open limit switch LS4. The limit switch LS4 is carried on the machine bed I8 and is positioned to be engaged and actuated into closed position by a cam 86 on the table 12 when the latter is moved to bring the wheel 32 exactly over the roll 36.

Also connected between the lines L3 and L4 is the contactor coil B which is in series with the normally closed blades 02 of the contactor C, the normall open blades A4 of the contactor A, and the normally open push button 86. The switch 88 is bypassed by the normally open blades Bl of the contactor B. The contactor B also comprises the normally open blades B4 in series with the motor 58 to control the energization thereof and the normall open blades B5 in circuit with the switch SI for controlling the effectiveness thereof during a dressing cycle.

Operation In operation, a dressing cycle is normally oommenced by closing the switch 84 whereupon the contactor A is energized. Energization of the contactor A closes the blades AI thereof to establish a holding circuit for the said contactor, opens the normally closed blades A2 to disconnect the armature 66 from the high voltage direct current line L3, and closes the normally open blades A3 in order to shunt the braking resistor 10 across the armature 66. The energization of the field coil 62 continues so that the closing of the braking circuit quickly brings the armature 66 to a reduced speed or to a halt.

Energization of A also closes the blades A4 so that the circuit to coil B is conditioned to permit energization thereof when switch 88 is closed.

Thereafter, the table I2 is moved until the wheel 32 is directly over the roll 36. The wheel is then lowered, if necessary, by the hand wheel 26 in order to bring it against the roll under pressure. Thereafter, either the cam 54 is adjusted relative to the limit switch LS2 or the stop 52 is adjusted relative to the limit switch LSI in order to provide for a predetermined amount of down-feed of the wheel 32, and the' switch 88 is closed.

Closing of the switch 88 energizes the con- Energization of :the a coil B also closes the blades lip.Simultaneously,the blades B3 are opened to interrupt" the dynamic-braking circuit-across the armature. Also, simultaneous with the energization of a contactor B, the blades B4 and B5 are closed the former toenergize the motor 58 and the latter to close the circuit through the switch SI and the solenoid 42.

Energization of the motor 58 commences rotation of the cam 56 in order intermittently to close the switch SI and thereby intermittently to energize the solenoid 42 to effect spaced increments of down-feed of the wheel to the desired extent. When the wheel has been fed down the desired amount either the switch L8! or the switch LS2 is closed by its associated cam to energize the coil C thereby opening the blades Cl and C2 thereof, the former to prevent further energization of the down feeding solenoid 42, and the latter to deenergize coil B to restore the electrical circuit to its condition prior to the energization of coil B. The closing of B2 and the opening of B3 which connected the armature 66 and coil 68 across the rectifier bridge 18 brings about a supply of low voltage direct current power to the said armature and field coil which causes the motor to operate at low speed thereby to drive the grindingwheel 32 in rotation. This rotation of the grinding wheel accomplishes the crushing thereof in connection with the down-feeding of the saddle and wheel toward the crushingvroll.

A new grinding cycle may be commenced after the dressing cycle is completed by depressing the switch 82 in order to de energize the contactor coil A and to reconnect the armature 66 and field coil 68 of the motor 30 across the high voltage direct current supply lines L3 and L4. It will be noted that to accomplish the foregoing step it is necessary to shift the table I2 to separate the wheel and roll in order to disengage the cam 86 and limit switch LS4. This positively prevents energizing the wheel motor to run at grinding speeds while the wheel and roll are together and likewise prevents the wheel and roll from being brought together while the said motor is running at grinding speed.

It will be apparent that this invention provides a ready means of operating a direct current motor at low speed by supplying thereto direct current power at reduced voltage, the sa d power being applied to the motor armature. The aforementioned supply of power is substantially inexhaustibly large by being taken from commercial alternating current lines through a step-down transformer and a rectifier bridge. This arrangement further insures that the low voltage direct current power will be at a constant voltage so that the speed of the wheel is substantially constant thereby insuring uniform dressing thereof by the dressing roll.

It will be understood that this invention is susceptible to modification in order to adopt it to difierent usages and conditions and, accordingly, it is desired to comprehend such modfications within this invention as may fall within the scope of the appended claims.

I claim:

1. In combination; a direct current motor; a high voltage and a low voltage drect current supply means for said motor; a braking resistor connected in circuit across the armature of the motor, means connecting the motor with the high 'voltage'supply including a] first contactor means selectively operable toconnectthe armature with the high voltage supply means andto disconnect the armature oi the'motor ifrom the high voltage supply and for connecting" the braking resistor thereacross; second contactor meansconnected in circuit with said braking resistor and connected with said low voltage supply means and selectively operable to open the braking circuit across the armature and to connect the armature to the low voltage supply, and a normally open switch in series with-said second contactor means and arranged to be closed by said first contactor upon energization thereof.

2. In combination; a direct current motor; a high voltage and a lowvoltage direct current supply meansfor said motor; a braking circuit including a resistor connected in circuit across the armature of the motor; means connecting the motor with the high voltage supply including a first contactor means selectively operable to connect the armature with the high voltage supply means and to disconnect'the armature of the motor from the high voltage supply and for connecting the braking circuit thereacross; second contactor means connected in circuit with said braking resistor and connected with said low voltage supply means and selectively operable to open the braking circuit across the armature and simultaneously to connect the armature to the low voltage supply; and switch means actuated by said first contactor for preventing the operation of said second contactor until the first contactor is energized.

3. In a grinding machine having an abrasive grindin wheel to be dressed and during which dressing the grinding wheel of the machine is operated at low speed; a. direct current wheel driving motor; a braking resistor; a high voltage direct current supply; an alternating current supply, a rectifier connected to receive power from said alternating current supply and to supply low voltage rectified current; first contactor means having circuit with said motor and with the high voltage supply and with said resistor and selectively operable at the beginning of the dressing of the wheel to disconnect the armature of said motor from the high voltage supply and for shunting the braking resistor across the armature; and second contactor means in circuit with said first contactor and having circuit with said resistor and with the rectified current and operable only after operation of said first mentioned contactor means to interrupt the braking circuit across the armature and to connect the armature across the rectified voltage supply.

4. In a grinding mach'ne having means for receiving an abrasive grinding wheel; a table reciprocable relative to the wheel; a dressing station on the table, including a device to dress said wheel, the dressing of said wheel being carried out at reduced wheel speed with the table positioned with the wheel at the dressing station; a compound wound direct current wheel driving motor including an armature and a series field connected therewith; a braking circuit includin a resistor shunting the armature of the motor; a high voltage direct current supply connected with the motor for operation thereof at rated speed; an alternating current supply, a step down transformer and a rectifier for supplying low voltage rectified current; a first contactor having circuit with said motor and with said braking circuit to disconnect the armature or the motor 7 and the series field of the motor from the direct current supply and to connect the braking circuit across the armature; a second contactor having circuit with said rectifier and with said braking circuit to interrupt the braking circuit and to connect the armature and series field to the low voltage supply; and a plurality of serially arranged independently operated switch means interlocking the contactors whereby the second thereof can be energized only upon closing of all of the serially arranged switch means.

5. In a grinding machine having means for receiving an abrasiv e grinding wheel, a table reciprocable relative to the said means for the wheel, a dressing station on the table including a device to dress said wheel, the dressin of said wheel being carried out at reduced wheel speed with the table positioned with the wheel at the dressing station; a compound wound direct current wheel driving motor including an armature and a serges field connected therewith; a braking circuit including a resistor shunting the armature of the motor; a high voltage direct current supply connected with the motor for operation thereof at rated speed; an alternat'ng current supply. a step down transformer and a full-wave rectifier for supplying low voltage rectified current; a first contractor having circuit with said motor and with said braking circuit to disconnect the armature and series field of the motor from the direct current supply and to connect the braking c rcuit across the armature; a second contactor having circuit with said rectifier and with said braking circuit to interrupt the braking circuit and to connect the armature and series field to the low voltage supply; switch means in circuit with said first contactor and engageable by said table to automatically actuate the first contactor when the table is in the dressing station; and switch means in circuit with said first contactor and said second contactor positively preventing the actuation of the second contactor prior to the actuation of the first contactor.

6. In a grinding machine having means for receiving an abrasive grinding wheel, a table reciprocable relative to the said means for the wheel, a crush dressing roll carried on the table; a compound wound d'rect current motor connected for driving the grindin wheel; a braking circuit including a resistor shunting the armature of the motor; a direct current source 'of electric power to drive the motor at grinding speed; an alternat'ng current supply, a step down transformer to reduce the voltage of the alternating current supply and a full-wave rectifier to rectify the output of the transformer; a first contactor having circuit with said motor and with said braking circuit to disconnect the armature and series field of the motor from the direct current supply and to connect the brak'ng resis-,

tor across the armature for rapidly reducing the speed thereof; a second contactor having circuit with said rectifier and with said braking circuit to interrupt the brakin circu t and to connect the armature and series field to the output of the rectifier; switch means in circuit with said first contactor and engageable by said table and automatically operable by said table when said table is positioned placing the wheel over the roll to energize the first contactor, thereby preventing the movement of the wheel into the roll at grinding speed; switch means rendered active by the energization of the first contactor to condition a circuit for the energization of the second contactor; sw.tch means actuated by said table when in position with said wheel over said roll to energize the second contactor; and feeding means rendered active by the energization of the second contactor for feeding the wheel and roll together a predetermined amount.

7. In a grinding machine having means ior hav ng circuit with said motor and with said braking circuit to disconnect the armature and series field of the motor from the direct current supply and to connect a braking resistor across the armature for rapidly reducing the speed thereof; a second contactor having circuit with said rectifier and with said brakng circuit to interrupt the braking circuit and to connect the armature and series field to the output of the rectifier; switch means in circuit with said first contactor and engageable by said table and automatically operable by sa d table when said table is positioned placing the wheel over the roll to energize the first contactor, thereby preventing the movement of the wheel into the roll at grinding speed; switch means rendered active by the energization of the first contactor to condition a circuit for the energ zation of the second contactor; switch means actuated by said table when in position with said wheel over said roll to energize the second contactor; feeding means rendered active by the enzrgization of the second contactor for feeding the wheel and roll together; and switch means actuated by a predetermined feed ng together of the wheel and roll for automatically de-energizing the second contactor to halt the dressing cycle.

JOHN C. WILSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

